Don't think it matters in the least bit. The only way a ressie would help you at Mears is if you needed a Wheelchair accessible van. There are only a few of those, so if you have a reservation, they try to make sure one is at MCO when your plane arrives. For everyone else, the only scheduling done is through the dispatcher outside.
I pre-purchased my tickets through Mears once, and all it did was save me paying at the airport. I still had to bring my confirmation sheet to the ticket counter so they could print my ticket, then take the ticket to the dispatcher outside.
So the process is no different.
Carol